April 30, 2010

FEATURE | Building Envelope

Halsall Associates begins second part of brick study

Masonry technology goes back to school for energy testing

DAN O’REILLY

correspondent

A two-part study measuring the impact of interior insulation on solid masonry walls may provide some solutions on how to effectively and safely bring Canada’s extensive inventory of older buildings up to modern day energy efficiency standards.

That inventory is a tremendous opportunity to reduce our environmental impact if those buildings can be given renewed life and lessen the need for new construction, explains James Wilkinson, project manager for Halsall Associates which is conducting the study.

He says the size of the opportunity is demonstrated by the increased application—or at least interest—in interior insulation/retrofit strategies by both public and private sector owners of buildings with solid or load-bearing masonry walls, says Wilkinson.

“Often these buildings have a heritage or historical significance that precludes work from the exterior. And even when it’s not a heritage building, many institutional owners don’t want the original masonry hidden.”

Insulating a masonry building from the interior, however, presents its own set of challenges. It may result in accelerated masonry deterioration, corrosion of the embedded steel, interior plaster finish deterioration and possibly mould growth.

That challenge is the basis for the study which Halsall is conducting at a Toronto private school. It includes the use of mock up walls in a classroom, temperature sensors, the physically testing of bricks and extrapolated computer generated weather and climatic conditions.

The institution wants to improve the energy performance of its buildings which includes a three-storey school built in the 1950s where the research is being conducted.

Common materials used to insulate masonry walls include traditional fibreglass, open-cell spray-foam insulation and closed cell spray-foam insulation. Each has its own specific risks and benefits, says Wilkinson.

For this study Halsall focused on the use of the closed cell spray foam insulation without supplying conditioned air to any of the wall cavities. Four mock up walls were constructed on the top floor of the school and at outside corner facing south and east. The exterior walls are three wythes thick and the interior is finished with hollow clay tile and painted plaster.

HALSALL ASSOCIATES

Sensors installed in a masonry wall are seen at top; below, an instrumented and insulated mock-up wall awaiting drywall.

The mock ups included two non-insulated and two insulated wall assembles. Nine sensors were installed in each to calculate temperature, relative humidity and moisture content at various locations. Driving rain was measured on the exterior south and east-facing exterior walls, while interior temperature and humidity were also measured at two locations within the test room.

Therae were a number of significant findings reached during the first stage of the study, conducted from Sept. 2007 to the same period in 2008.

A key discovery was that the insulated walls demonstrated a low freeze-thaw deterioration risk when compared with the non-insulated walls. There was, however, a minor risk of embedded metal corrosion.

The study also concluded the bricks were highly moisture absorptive and didn’t meet modern CSA standards for freeze-thaw resistance performance. In reality, though, the bricks are functioning properly and haven’t exhibited signs of deterioration, says Wilkinson “They look okay.”

This first stage study wasn’t considered conclusive enough because the monitoring period was marked by a mild winter and less-than-normal rainfall.

Those limitations were the catalyst for a follow up second study which started last September and scheduled to wrap up this May.

If the weather doesn’t co-operate, the Halsall testers will do hydro-thermal modeling, says Wilkinson.

At this point the institution has not committed to a major retrofit/insulation and the final conclusions should not be considered as blanket remedy that can apply to all masonry buildings.

The study’s methodology can be used as process to evaluate the pros and cons of interior insulation, he says. “Each project would have to be done a case by case basis.”

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